Chalk Range

January 25, 2019

As a word, ‘chalk’ has come a long way from its geological origins, only to develop a rather undistinguished association with school blackboards and hopscotch. Of course, its original meaning is still part of common parlance in places where chalk forms a significant element of the underlying geology (as in parts of England and Europe).

However, chalk is not a common stone type in New Zealand, where we are more accustomed to other types of limestone than this soft, friable, uniform material. Accordingly, Marlborough’s Chalk Range sits as a notable oddity amidst the wider landscape, and its title has a somewhat exotic air to it.

Chalk Range’s distinctive geological makeup (which varies considerably over the range, and consists of material that is better described as ‘chalky’ rather than pure chalk) has provided the conditions for species to evolve that are endemic to the range (such as the critically endangered Pachycladon fasciarium), as well as for other species with limited natural distribution.

One intriguing example of the latter is an attractive, silver-leaved forget-me-not, Myosotis arnoldii, which naturally occurs on the distant points of Chalk Range (and a couple of nearby localities in Marlborough) and Hoary Head (a marble dome in Nelson’s Kahurangi National Park).

Another nationally rare species found on Chalk Range is the limestone broom, Carmichaelia astonii, which (in contrast with the aforementioned forget-me-not) we saw in large numbers on and around a particularly interesting series of cliffs. This highly attractive dwarf shrub has large flowers in comparison with other native broom species, and their effect is further amplified by the diminutive stature of the overall plant.

C. astonii grows out of crevices in both the vertical face of outcrops and on the pavement-like surface on the tilted ridgeline – as shown below, where mats of Carmichaelia astonii emerge from the cracks of the mostly solid limestone. It would appear that the new growth of limestone broom is appealing to browsing animals (rabbits are probably a major culprit), as more accessible specimens such as those shown below looked distinctly chewed in comparison with plants emerging from the fractured cliff faces.

We were keen to find (and more importantly, identify) a recently-described species of native daphne associated with limestone substrates, called Pimelea aridula ssp. oliga, which is recorded from this range. However, despite having spent a lot of time observing Pimelea aridula ssp. aridula in the wild in Central Otago, we were unable to decide for sure whether we were looking at P. aridula ssp. oliga or the similar P. concinna. The leaves of one of the mounded hummocks of Pimelea that we encountered at various points along Chalk Range are pictured below, left.

Rob’s fascination with the spectacular weeping form of Myrsine divaricata (pictured above, right) was indulged when we stopped by the extremely steep forested slopes that occur towards the middle of the range. In line with other forests from highly drought-prone areas in the south of New Zealand, this forest is dominated by Hall’s tōtara, with Griselinia littoralis, Coprosma linariifolia and Myrsine divaricata playing significant roles within the understorey and along the forest edge.

Parsonsia capsularis was in flower along the forest margin, with the attractive pink flower colour that this species often bears in the South Island. Aside from its profusely-borne flowerheads, I was also interested in the very narrow leaf that these specimens retained throught to their adult phase. Although southern forms of native jasmine (Parsonsia) tend to retain a narrower leaf when mature, these possessed a particularly fine texture.

Having noted Rob’s near-obsession with Myrsine divaricata, it is only fair to even up the stakes by mentioning my own fascination with vegetation types that elude typical notions of ‘natural’ and ‘artificial’. As with other groves situated within pastoral (or pseudo-pastoral) settings, this kind of ambiguity is displayed perfectly by the groves of Hoheria lyallii through which we climbed and descended.

This beautiful, compact, white-flowering native tree of the South Island’s eastern flank already bears an appearance that seems atypical (even exotic) within the communities in which it occurs – due to the similarity of its silvery leaves to poplars. When viewed in pure groves, this sense of foreignness is magnified by the silver trunks and branching form, which bring to mind European birch woodlands.

Returning to the name of the range itself, ‘chalk’ quite literally translates as ‘limestone’, as one can surmise from the German word for limestone, ‘Kalk‘ – which is in turn derived from the Latin word for limestone, calx. New Zealand has a rich diversity of areas characterised by both limestone and metamorphosed limestone (such as marble and dolomite).

The particular nature of these substrates provides various platforms for the process of evolution to generate new species and forms – many of which (such as the limestone kowhai, Sophora longicarinata, or the diminutive marble endemic, Clematis marmoraria) are significant for horticulture.